Yesterday i decided to upgrade my installation of SQL Server 2012 (on Windows 10 professional) with the most recent serivice pack, the sp4. Everything works fine, until the at some step before completation, the setup ended wid the error:

Wait on the Database Engine recovery handle failed. Check the SQL Server error log for potential causes.

This error, leaved the sql server in a unstartable state. None work to recover the installation.

At this point, i decided to download and install a fresh copy o SQL Server 2016 developer edition. But also this setup failed with the same error. Every suggested solution do not works. At some point reading the SQL Server installation log, i found this line:

The code page 65001 is not supported by the server

What the hell?

After some search, i discovered that there is a new (beta) option in Windows 10 April 2018 update:
Beta: Use Unicode UTF-8 for worldwide language support

Basically this option force to use UTF-8 (65001 character set) in every windows function. But the secondary effect is that old(?) setup do not works anymore. To disable this option:

control panel->regional settings->administrative->change system locale

uncheck the option.

After that every setup works with no problem.